Too early to say whether the white cliffs of Antarctica are unstable

“Antarctica meltdown could double sea level rise”, went the headlines in 2016, “runaway melting” predicted by “alarming science”. They were reporting a new study that predicted the ice cliffs along the coasts of Antarctica could crumble far more rapidly into the ocean than previously thought, raising sea level this century by a metre or more. Understandably, it was reported more than any other climate study that year. But how likely is the apocalyptic scenario predicted by Rob DeConto and Dave Pollard, and how soon?

Too early to say, judging by the Met Office’s UK Climate Projections 2018 published today. This is an enormous report, written to inform UK Government planning for climate change, and it covers far more than sea level rise alone. I was involved in writing the Marine Report, but not in the number-crunching they did to calculate their new sea level projections.

Their top line: slightly higher sea level rise than was predicted in the last major IPCC report of 2013. Fourteen more centimetres this century for the upper end of the worst case scenario, raising it to 112 cm by 2100. (Here ‘worst case scenario’ means about the highest greenhouse gas concentrations we can imagine.) Fourteen percent more rising of the future seas.

Not double, in other words. The text – again, full disclosure, which I co-authored – says the key processes in the 2016 study were simply represented and are still poorly understood, and that their triggering by future warming is uncertain. The Met Office scientists decided to use an older study of Antarctica led by Anders Levermann instead: one that does not include this catastrophic ice cliff collapse, and that agrees with other studies published since the IPCC. A bit higher, but not much. The news is bad, but could have been worse.

Incidentally, the UK Climate Projections 2018 for London and Cardiff are very slightly higher than for the global average (upper end 113-115 cm), while those for Edinburgh and Belfast are lower (90-94 cm). This is because northerly parts of the UK are still rising up after the local ice sheets of the last ice age melted, while the southerly parts are slightly sinking, creating a see-saw effect.

UKCP18 has particular meaning for me, as the second bookend of my career in climate. The last report, UK Climate Projections 2009, was the first. In my first climate job, PalaeoQUMP (2006-2010), I worked with many of the Met Office authors of UKCP09, learning how to assess climate model uncertainties from those making the most sophisticated assessment so far. I took these methods and started using them for ice sheet models. The collaborations, methods and friendships have lasted over a decade.

The story of Antarctica will undoubtedly continue, as we improve our computer models and gather more observations of the ice cliffs. I have my own skin in the game: I will hopefully be able to write about this here early next year.

Talking of skin in the game, thank you for all your kind messages this year, and your donations to my Bowel Cancer UK campaign, raising an incredible £6500. (I could have done with some UK Bowel Cancer Projections 2018…). I am slowly starting to recover from chemotherapy – frustratingly slowly! – and it is good to be back to work and lecturing, even when it is exhausting. Is my health ‘unstable’? Too early to say, I guess. Clear scan in August. The news this year was bad, but could have been worse.

This post has been edited to reflect the fact that the ‘upper end’ of the projections does not correspond to a particular probability.